[PATCH 0/3] Improvements to Python parameters

[Tom Tromey]

This series fixes a few problems with gdb parameters when used from
Python.

Currently, gdb captures the current language on entry to Python.
However, this means that Python scripts can't affect this setting in a
meaningful way.  However, that is bad because such scripts are often
dependent on the current language -- for example, for symbol lookup or
expression evaluation.

I also found some crashes involving parameters.  The second patch in
particular tries to make such crashes harder to introduce.

Finally, this adds a convenience API to make it easy to temporarily
modify a gdb parameter for a block of Python code.

Let me know what you think.  I'm particularly interested in whether
the API is reasonable.

Regression tested on x86-64 Fedora 34.

Tom